Trip steel for springs

ABSTRACT

THIS INVENTION RELATES TO ELASTIC ELEMENTS, PRIMARILY SPRINGS ON WHICH THE REQUIRED STANDARDS OF FATIGUE RESISTANCE AND/OR FLATNESS, ETC. ARE OF A HIGH ORDER. MORE SPECIFICALLY, THIS INVENTION RELATES TO SPRINGS WHICH ARE PRODUCED FROM A STEEL ALLOY, THE COMPOSITION OF WHICH IS SUCH   THAT IN A TEMPERATURE RANGE BETWEEN 500 AND 700*C. THE STEEL MAY HAVE A MATRIX THAT IS PRIMARILY FERRITIC.

p 1974 1 KLAS-ERIK JAKENBERG 3,834,951

TRIP STEEL FOR SPRINGS Original Filed June 17, 1968 2 Sheets-Sheet 1 FIG. lo

Sept. 10, 1974 KLAS-ERIK JAK-ENBERG 3,834,951

TRIP STE-BL FOR SPRINGS Original Filed June 17, 1968 2 Sheets-Sheet 2.

Fl G.7b

United States Patent Int. Cl. C2 1d 9/02 US. Cl. 148-36 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to elastic elements, primarily springs on which the required standards of fatigue resistance and/or flatness, etc. are of a high order. More specifically, this invention relates to springs which are produced from a steel alloy, the composition of which is such that in a temperature range between 500 and 700 C. the steel may have a matrix that is primarily ferritic.

This application is a continuation of Ser. No. 737,779, filed June 17, 1968, and now abandoned.

In many cases, the required standards of fatigue resistance and flatness, etc. in respect to elastic elements are extremely high. In addition to this, it is often required that the elements exhibit good corrosion resistance and the ability to retain their favourable properties even at high temperatures. Further, high uniformity of quality is often desired, as for example for springs in precision instrumeans.

The hitherto prevalent method of producing material for springs of the type concerned here has in principle consisted of hot and cold rolling, hardening, annealing and polishing, i.e., a series of entirely conventional processes. High quality in the raw materials has naturally been required, and this has consisted of high-grade steel produced from ores of a very high degree of purity which give a steel free from undesirable elements and impurities. Further, great importance has been attached to process control as well as examination of the finished product.

It has also been realized that a structure containing a large number of fine carbide grains in the material before hardening is extremely desirable. A structure of this kind has been found to improve hardenability. If hardening can be performed faster, a finer martensitic structure is obtained and thereby also a material with improved fatigue properties.

However, producing a material with a large number of fine carbide grains (more than 40 carbides per 100 ,ul'Il. and preferably more than 60 carbide grains-so-called pin-point structure) has been associated with certain difiiculties. Thus the unavoidable annealing operations in conjunction with cold rolling entail a progressive grain growth. Further, the repeated heating operations give rise to structural variations in a cross-section of the strip as Well as in different portions of it, a circumstance that may affect the flatness of the strip.

According to this invention these disadvantages in the spring material can be eliminated by using a strip that has been rolled in a ferritic state in the temperature range 500790 C. with not less than 40% total reduction in area, whereby the processing temperature and reduction are so adapted that a structure substantially of finelydispersed spheroidized carbides in a ferritic matrix with not less than 40 and preferably not less than 60 carbide grains per 100 ,um? is obtained. The thickness of the strip has preferably been adjusted to the desired dimension by a subsequent cold rolling operation. Recrystallization annealing due to cold-hardening during this final rolling operation is not always necessary and in cases where it must be resorted to may be limited to one or two annealing operations, which cannot to any appreciable degree affect the quality of the final product. The strips are 3,834,951 Patented Sept. 10, 1974 ice also hardened, annealed and polished in the conventional manner.

The spring material according to this invention may thus in a simple way be made superior in quality to that previously produced, while at the same time the process confers great advantages in processing techniques, which leads to a less expensive product. Inasmuch as the utilization according to this invention may find application in many spheres where there is a need for elastic elements of high quality, some typical examples will be given in the following with reference to appended Figs.

EXAMPLE 1 Application for flapper valves Spring steel in strip form is used for flapper elements in flapper valves where the requirements in respect of fatigue resistance and wear resistance as well as good flatness are exceptionally high in order to ensure perfect sealing throughout the life of the valve. Some typical embodiments of such flapper elements are shown in FIG. 1.

The elements shown in FIG. 1 can be suitably made of Uddeholm grade UHB 20 steel, a carbon steel With 1.0% C and with very low impurity content. According to this invention, strip material that has been rolled in the temperature range 550-720 C. with such severe plastic deformation that so-called pin-point structure is obtained is used in the manufacture of valve elements. This means that the structure shall consist of fine-grain, spheroidized carbides in a ferritic matrix with not less than 60 carbides per 100 m Processing at the higher temperatures is normally followed by adjustment rolling at room temperature. Cold rolling in itself does not therefore constitute a condition for the attainment of the desired structure but should only be regarded as an operation normally necessary for other reasons.

For UHB 20 the most suitable working temperature is 700 C. The initial material consists of hot-rolled and subsequently descaled strip which shall have a lamellar pearlitic structure. At the working temperature of 700 C. the total reduction in area should be not less than 7% in order for the desired spheroidizing time to be attained. A higher value of for example, is nevertheless more suitable. The structure of UHB 20 that has been rolled with 77% reduction in area is shown at a magnification of 1,200 in FIG. 7a. Furnace temperature was 700 C. The structure is at the limit of what can be described as pinpoint.

FIG. 7b shows the same steel that has been rolled down to a total area reduction of 84.2%. Furnace temperature in this case was also 700 C. The temperature of the strip had fallen to 665 C. in the final pass. The structure consists of well-spheroidized carbides in a ferritic matrix with 68 carbide grains per 100 ,um. and thereby satisfies well the requirements of pin-point. The good homogeneity of the structure, which is decisive for the flatness of the spring steel, will be evident from the photograph.

Lower processing temperatures require greater reductions in order to attain complete spheroidization. FIG. 8 shows, at a magnification of 1,200, UHB 20 that has been rolled with a total area reduction of 81.4%. Furnace temperature 600 C., final temperature 540 C. Pin-point structure has certainly been obtained, but the structure still contains residues of lamellar perlite. This is not desirable due to the requirement of homogeneity, and for this reason the total reduction at this temperature should be not less than 85% and preferably The thickness of the strips from which flapper elements of the types shown in FIG. 1 are to be punched after rolling at temperatures between 550 and 720 C. with subsequent adjustment rolling at room temperature shall be approximately 0.10.6 mm. After adjustment rolling the steel is hardened, tempered and polished.

Flapper elements of the type described in Example 1 can be utilized a.o. for flapper valves in refrigerating units and air-conditioning equipment of various kinds as well as in non-corrosive or only mildly corrosive media.

EXAMPLE 2 Application for flapper valves in corrosive media For corrosive media a stainless steel must be resorted to such as Uddeholm UHB Stainless 716 steel, which has the type analysis 0.35% C, 13.6% Cr, 1.0% Mo. FIG. 2 shows a flapper valve in a two-stroke engine, i.e. in a corrosive medium at high temperature. According to this invention the strip steel used for the flapper element is of UHB Stainless 716 type, which with a lamellar initial structure has been rolled within the temperature range 700-790 C., suitably at approx. 760 C. As in Example 1, temperature and the degree of reduction are adapted in relation to each other so that a well-spheroidized structure with not less than 60 carbide grains per 100 ,um. is obtained. In this case adjustment rolling at room temperature is also undertaken with one of two annealing points as well as hardening, tempering and polishing whereby, which is the important advantage of pin-point, hardening can be performed extremely quickly so that an extremely fine martensite is obtained.

The thickness of the strip from which the flapper elements are punched is the same as in Example 1.

EXAMPLE 3 Application for feather valves Strip steel for feather valves is usually supplied in widths corresponding to the width of the reeds in the valve and is therefore provided with rounded edges. Feather valve steel is characterized by high requirements as to fatigue resistance and accurate flatness, straightness and surface finish in order to ensure good sealing against the valve seat. Normal thicknesses are 0.3-1.0 mm. and widths -25 mm.

A suitable steel is the aforementioned UHB 20, which according to this invention is used in the state described in detail in conjunction with Example 1, although in somewhat thicker dimensions.

Another steel that is suitable for non-corrosive media is Uddeholm UHB 15N20 steel with the type analysis 0.75% C and 2.0% Ni. According to one embodiment according to this invention, UHB 15N20 which in the form of strip has been rolled at approx. 700 C. whereby the total reduction in area has been carried so far that a spheroidized structure with finely dispersed carbides numbering not less than 60 per 100 m? has been obtained, is used for the reeds in feather valves. An area reduction of not less than 70% is suitable and preferably even greater than 85%. After the massive reduction at approx. 750 C., cold-rolling, rapid-hardening, tempering and accurate polishing have been carried out.

EXAMPLE 4 Application for feather valves in corrosive media Requirements in respect of the physical properties of the reeds are the same as in the previous example. In addition to this is the requirement of corrosion-resistance. A steel analysis that has previously been utilized and which can also be utilized according to this invention is the UHB Stainless 716 mentioned in Example 2 and also the Uddeholm UHB Stainless 31, which has the composition 0.22% C, 13.6% Cr and 0.5% Ni.

According to this invention, the steel processed in the manner described for UHB Stainless 716 in Example 2 is used, taking into due consideration, however, the thicker dimensions mentioned in the previous example.

EXAMPLE 5 Application for compressor valves Compressor valves usually incorporate elastic elements in the form of cushion plates, valve plates and rings of various designs. FIG. 3 shows a typical embodiment of a valve ring intended for use in a compressor valve. The most important properties of the elastic elements in a compressor valve are high fatigue resistance and wear strength as well as good flatness. The thickness dimensions vary between 0.3 and 1.0 mm. For non-corrosive media, the UHB 20 and UHB 15I\'20 steels previously mentioned may be used, for example.

According to this invention, one of the aforementioned steels which has been processed in the manner described iinlExamples l and 3 is used for the above-mentioned For corrosive media a stainless material is used instead, such as one of the previously mentioned UHB Stainless 31 or 716 steels. In the use of these materials according to this invention, the strip material shall be processed in the manner that has been previously described in Examples 2 and 4, through which the stated requirements can be fulfilled.

EXAMPLE 6 Application for scavenge valves FIG. 4 shows the appearance of a blade valve for scavenge pumps. In the Fig. the valve is disassembled and the appearance of the elastic elements incorporated in the valve will be evident from the detail in the righthand part of the Fig. The chief requirement in elements of this kind is very good flatness, so that perfect surface contact is obtained even in very large elements. Common thicknesses are between 0.3 and 0.7 mm. UHB 20, UHB 15N20 and UHB Stainless 31, for example, have suitable compositions, whereby the choice of material will have to be decided by the medium in which the valve is intended to operate.

According to this invention, one of the aforementioned steels is used, for example, which in strip form has been processed in the manner described in conjunction with the previous examples, through which the high requirements of flatness can be attained.

EXAMPLE 7 Application as shock absorber plates FIG. 5 shows four shock absorber elements intended for different functions in one and the same shock absorber. Excellent spring power and good flatness are chiefly required of elements of this type. Normal thicknesses are up to 0.6 mm. and widths up to mm.

UHB 20 with type analysis 1.0% C has a suitable steel composition, which according to the invention is rolled in ferritic state at 700 C. with such massive reduction that a chiefly pin-point structure is obtained, after which the thickness is adjusted and the surface improved by a cold-working operation. The strips, which due to the pinpoint structure it has been possible to quick-harden, are also annealed and polished in the usual manner after hardening.

EXAMPLE 8 Application for so-called roller springs The roller spring is a new machine element which is expected to be able to give possibilities of new solutions to difficult constructional elements, at least in connections where smaller forces are sufficient. FIG. 6 shows in a schematic way how a flat spring under tension is folded around two rollers in a frame. The diameters of the rollers are large enough to prevent them passing each other in the frame.

This device has been given the name Rolamite. The spring which has been hardened in a flat state endeavors to straighten out and the two loops around the rollers act on these in the opposite direction. The repeated bending is a drawback involving severe fatigue stress. As a remedy, it has therefore been necessary to reduce the bending stress by keeping the spring as thin as possible. This, on the other hand, has resulted in that the device has only been able to be used where the forces are small, such as in the manufacture of instruments, for example.

If the spring is made according to this invention instead of a strip which has been rolled in ferritic state at a temperature in excess of 550 C. with such severe deformation that a pin-point structure is obtained, the field of application of the roller spring can be considerably widened as a result of fatigue resistance being improved so that no major reduction in dimensions need be undertaken.

The aforementioned UHB 20 steel, for example, has a suitable composition for roller springs, and for corrosive media UHB Stainless 31 is suitable. According to this invention the materials are intended for use in the state as described in conjunction with the previous examples.

Other fields where springs according to this invention may find suitable applications are for coil springs such as used in clocks, cine-cameras, scientific instruments, relay equipment, etc. as well as for flat springs in apparatus of various types.

It should be realized that this invention can be varied within the scope of the inventive idea. The stated steel compositions are only to be regarded as conceivable examples of analysis types which may be used according to this invention. Different additives are consequently quite conceivable. The steels should preferably be hardenable. Unalloyed steels should have a carbon content in excess of 0.4% and alloy steel which within the stated temperature range shall have a ferritic matrix with carbides in various configurations, should preferably have a carbon content in excess of 0.2% and different matrices commonly occurring in steel. According to this invention material containing such substances as favour the formation of graphite, such as silicon, nickel and aluminium, so-called fine-grain steel, i.e. material that in conventional techniques would have presented great difficulties in conjunction with cold-working and annealing, can be used to advantage. It is also possible, for steels which in conventional processing are prone to the formation of graphite, by additions of the deoxidants aluminium and silicon in contents up to 0.1% and 2%, respectively, to manufacture steel with a lower slag content.

I claim:

1. A spring element made from a steel strip, the steel having, at least in a portion of the temperature range between 500 and 700 C., a ferritic matrix, in which range the steel strip in the ferritic state of the steel has been rolled with not less than total reduction thereby acquiring a structure of finely dispersed spheroidic carbides in a ferritic matrix with not less than carbide grains per mF.

References Cited UNITED STATES PATENTS 2,801,916 8/1957 Harris et al. 148-12 2,905,577 9/1959 Harris et a1. 14812 3,116,180 12/1963 Malzacher 14812.4 3,216,868 11/1965 Nachtman 14812 3,281,287 10/1966 Edstrom 14812.4 3,423,252 1/1969 Grange 14812 3,425,877 2/1969 Deacon 148-124 WAYLAND W. STALLARD, Primary Examiner US Cl. X.R. 

